Polyolefins are robust, flexible plastics which, on the basis of their ease of processing and chemical resistance, have numerous possible uses and, with a proportion of about 45%, represent the largest individual group of consumer plastics in Europe.
By far the largest sector for use of polyolefinic plastics is that of packaging. The omnipresence of plastic packaging brings it again and again under the spotlight of environmental debate. Absent any suitable infrastructure for collecting, sorting, and reutilization, plastic packaging can become a problem, as is made clear by the debate on the contamination of the oceans. In varying scope and to varying extents, such infrastructures have been built up across Europe in the past 25 years, initiated by the EU Packaging Directive and by the corresponding national legislation. In Germany this infrastructure is constituted by the interception systems of the yellow bag/yellow bin type and by the associated approaches and plants for sorting and reutilization. The long-term viability of these infrastructures and their expansion to other countries are dependent quite essentially on the demand within industry for recycled plastics; the higher the quality of the recyclates made available, the better the evolution of this demand will be.
In the case of packaging made from PET, this is already being done today in a closed loop, with packaging plastics being used again in the next usage cycle to produce packaging. With polyolefins, a problem which arises is that, from standard recycling processes, polyolefins are processed in mixed colors, which recur in the recycled material as well. Consequently, depending on the composition of the starting material, the end products produced accordingly have various shades of gray. Because the recycling processes available to date also leave residual contaminants on the polyolefinic plastics, the processed products are subject to giving off typical recyclate odors, which rule out near-end-user applications. As a result, in the case of polyolefinic plastics, the applications available are predominantly now “open-loop” applications more remote from the end user; in other words, the recyclates, rather than being processed into packaging again, are instead processed into long-life plastics products from—for example—the construction sector.
A particular hindrance to the renewed use of polyolefin plastics are extraneous substances which are picked up in small amounts during the primary use of the polyolefins. For example, polyethylene packaging for a shampoo may pick up apolar ingredients such as fragrances from the shampoo, which thereafter cannot be removed simply by washing with water. If a polyolefin recyclate of this kind is exposed to high thermal loads, as is the case with extrusion operations, for example, these migrant substances undergo decomposition, this being a substantial source of the typical adverse recyclate odors.
Another hindrance, particularly affecting polyolefin packaging material, is that this material is not received as a starting material of relatively uniform color—in contrast, for example, to PET beverage packaging. Employing the sorting methods which have been customary to date, this leads to products in various shades of gray, as mentioned above.
An exception to this are specific collecting systems for uniform packaging, in the form of milk bottles, for example, which, like other beverage packaging, is collected separately in supermarkets in Great Britain, for example. The majority of polyolefin packaging, however, which often comprises not only different-colored polyolefin packaging but also a significant proportion of other plastics and extraneous substances such as metals, wood or paper, is sorted merely according to the type of material (e.g., “PE”) and, as explained above, usually after having been comminuted and washed with cold water, is granulated and employed in consumer-remote applications at an earnings level which is usually well below the price for virgin product.
The long-term trend of rising raw-materials prices and also the pressure perceived within the consumer goods industry to adjust to a rising demand for sustainably produced products have given rise to a requirement for methods allowing polyolefinic packaging wastes, especially those from domestic households, to be processed for use again in packaging for end users. For this purpose, the method ought to provide an extremely cleansed recyclate product which can be sent for renewed extrusion, without generating byproducts afflicted by an unpleasant odor. Furthermore, the method ought to be able to be carried out with minimal complication, even at large throughput quantities, and inexpensively, to give a product which is competitive on the market. The present invention engages with this requirement.